A power assisted steering system of similar type, but having a cam and roller assembly instead of a nut and screw assembly, is known under the type-name "ZF-Gemmer Hydrolenkung". In this known steering system the input shaft is a rigid shaft capable of effecting, by means of a universal joint, a limited transverse movement upon being rotated. This transverse movement activates two or all of four discrete closing components provided in a control valve. Thus, the control valve and the means for activating it are of a rather intricate design, composed of a large number of parts.
Another power assisted steering system of similar type is described in the German published patent application No. 2,118,813 (DT-OS 2,118,813). In this known steering system is probably used a conventional rotary type control valve integral with the input shaft and activated by the torque applied to the input shaft. Also rotary type control valves are of a rather intricate design, and due to the design of the steering system high pressure seals are necessary for preventing oil of high pressure from leaking along the input shaft out of the steering gear housing.
Steering systems of the type comprising at least one flexible shaft having an input end driven by a step-up gearing and an output end driving a reduction gearing are disclosed in the French patent specification No. 2,171,815, and the present invention is specially applicable on said type of systems.
The object of the present invention is to provide a power assisted steering system, wherein the control valve and the means for operating it are of a simple design, and wherein simple low pressure seals can be used for preventing oil leakage along the input shaft.